he LIR is currently studying prospectively the largest group f patients with the vasculitic syndromes in the world. On the asis of clinical, pathophysiologic, immunopathogenic and herapeutic results obtained over the past 16 years, we have esigned a revised categorization scheme for the vasculitides hich has now reached worldwide acceptance. We have developed nd instituted aggressive chemotherapeutic regimens consisting f chronically administered cyclophosphadmide together with lternate-day corticosteroids in several, formerly universally atal diseases such as Wegener's granulomatosis. In this egard, we are now following over 100 patients with Wegener's ranulomatosis in which we demonstrated a 95% remission and ure rate. We have now applied these approaches with emarkable success to other of the vasculitic syndromes such as ystemic vasculitis of the polyarteritis nodosa group, isolated entral nervous system vasculitis, Takayasu's arteritis, and he acute vasculitis of Sjogren's syndrome. In addition, we tudied the pathophysiology of lymphomatoid granulomatosis and ave shown it to be a prelymphomatous condition which responds n its early stages to chemotherapeutic regimens used in the asculitic syndromes. Patients who responded in the early tage did not go on to lymphoma and remained disease free over ong-term follow-up. The patient populations studied in the asculitis protocol have been utilized to precisely delineate berrancies of lymphocyte activation and immunoregulation seen n these diseases. In addition, the precise effects of various herapeutic regimens, particularly corticosteroids and ytotoxic agents, on human lymphoid cells have been described. n this regard, we demonstrated the exquisite and selective ensitivity of certain phases of the B cell cycle to yclophosphamide therapy, an observation which might help xplain its efficacy in certain diseases characterized by yperreactivity of B cell function.